This invention relates to bacterial cellulose (BC) of which ribbon-shaped microfibrils are artificially modified to improve Young""s modulus and a method of producing the same.
The bacterial cellulose can be used as various industrial materials, clothing materials, materials for medical supplies, functional materials, materials for foods and so on.
It is known that Acetobacter xylinum ATCC 23769 produces a mat-shaped cellulose which can be used for medical pads (Japanese Patent KOKAI 59-120159). It is also known that Acetobacter aceti subsp. xylinum ATCC 10821, etc. produce bacterial cellulose composed of ribbon-shaped microfibrils (U.S. Pat. No. 4,742,164). The size of the ribbon-shaped microfibril is said to be 20 to 50 nm (Ed. by Tokyo Techno-Forum Secretariat, xe2x80x9cJinrui to Bia (Humanity and Bio)xe2x80x9d, P329, 1993, Yomiuri Nippon Television (enter) which may be measured without discrimination of the major axis (width and the minor axis (thickness).
The bacterial cellulose is produced as floc or suspended matter in a form of sheet, dispersion, grain or the like by static culture or aeration agitation culture which effects entangling of fibers. However, although the above macroscopic variation occurs, ribbon-shaped microfibril and properties of the bacterial cellulose are substantially not varied.
Structure and properties of bacterial cellulose are slightly different according to the type of bacterium. However it has not been reported to produce modified bacterial cellulose by changing the form of cellulose-producing bacteria artificially to vary ribbon-shaped microfibrils.
An object of the invention is to develop a bacterial cellulose, wherein the major axis (width) of ribbon-shaped microfibril is varied, and various properties, especially Young""s modulas are improved.
The inventors investigated in order to achieve the above object, and found that a modified bacterial cellulose wherein ribbon-shaped microfibrils are varied can be obtained by adding a cell division inhibitor or an organic reducing agent to a culture medium which induces variation of the shape of cellulose-producing bacteria, and that properties, especially Young""s modulus, are improved compared with conventional bacterial cellulose.
Thus, the present invention provides, bacterial cellulose comprising ribbon-shaped microfibrils having a thickness of 10 to 100 nm and a width of 160 to 1000 nm, a method of producing bacterial cellulose which comprises culturing cellulose-producing bacteria which produce the bacterial cellulose extracellularly in a culture medium containing a cell division inhibitor, and recovering the bacterial cellulose produced in the culture medium, and further the present invention provides bacterial cellulose comprising ribbon-shaped microfibrils having a thickness of 10 to 100 nm and a width of 50 to 70 nm, and a method of producing bacterial cellulose which comprises culturing cellulose-producing bacteria which produce the bacterial cellulose extracellularly in a culture medium containing an organic reducing agent, and recovering the bacterial cellulose produced in the culture medium.
In the invention, a section of a ribbon-shaped microfibril perpendicular to the growth direction (lengthwise direction) is assumed a rectangle, and one side is called the width or the major axis and the other side is called the thickness or the minor axis. In general, the length of the major axis is longer than the minor axis.
The microfibril of bacterial cellulose of the invention can be discriminated from conventional microfibrils by measuring the length of each major axis and minor axis using an electron microscope of atomic force microscope.
It is seemed that the shape or the number of cellulose secretion port varies due to the variation of the shape of the bacterium, and thereby, the shape of microfibril is varied. From experimental results, bacterial cellulose produced by long cell bacteria has a higher clarity than short cell bacteria, and the results suggest that the cellulose produced by long cell bacteria is in a more dense state. This is also supported by the observation of bacterial cellulose using a scanning electron microscope (SEM) and an atomic force microscope, and therefore, the cellulose produced by long cell bacteria has a more dense layer structure. In the conventional cellulose produced by normal bacteria, portions where cellulose is deposited in a helicoidal (cholesteric) form are observed,.but the portions are not present in the cellulose produced by long cell bacteria. As to crystal width, it is considered that the cellulose produced by long cell bacteria is, although slightly, greater than the cellulose produced by normal bacteria in all lattice planes. In all bacterial cellulose, 0.6 nm lattice planes are oriented against film face, the cells are greater, the orientation degree is higher. In the observation of bacterial celluloses using a transmission electron microscope (TEM), the width of ribbon-shaped microfibril produced by long cell bacteria is greater than that produced by normal bacteria.